1. Field of the Invention
The present invention relates to an arc welding process and apparatus for preventing the occurrence of pits and blowholes which are often times generated when steel plates coated with, for example, anti-rust paint, are butted together in a T-shape for horizontal fillet welding, thus obtaining an improved weld bead appearance.
In shipbuilding and bridge construction, a large portion of the weld joints are fillet welds, so that an automated fillet welding technique will improve upon the efficiency of the overall welding operation.
2. Description of the Prior Art
Gas shielded arc welding, submerged arc welding and other welding techniques are all capable of being automatically carried out. However, when fillet welding steel plates coated, for example, with anti-rust paint, the gas generated by the decomposition of the anti-rust paint causes pits and blowholes in the plates, thus requiring additional labor for repairs which decreases the efficiency of the operation.
Furthermore, during such horizontal fillet welding the generated arc is customarily not made coincident with the line of intersection between the horizontal steel plate and the vertical steel plate, but is instead directed at the top surface of the horizontal plate. Such is illustrated in the prior art, as shown in FIG. 1 wherein a vertical steel plate 1 is disposed in perpendicular fashion to a horizontal steel plate 2 and the fillet welding operation is carried out with the use of a power supply nozzle 3 supporting a welding wire or electrode 4. The center of the generated arc is normally off center from the line of intersection of the plates by a distance .times. of approximately 2mm from the vertical plate. The reason for this is that when the arc is directed toward such line of intersection, an undercut 5 of the weld bead 6 results in vertical steel plate 1, typically as shown in FIG. 2.
Moreover, it has been found that the above-mentioned deviation of the arc center by the distance .times. likewise causes the anti-rust paint of the horizontal steel plate to decompose at the butt section of the vertical steel plate and the horizontal plate, whereby the decomposed gas is contained within the weld bead, which itself develops pits and blowholes.